Device and method of sensing temperature of a rotating electromagnetic machine

ABSTRACT

A system and method of determining the temperature of a rotating electromagnetic machine, such as an electric motor or generator. A temperature calibration parameter is calculated based on the temperature of an object situated close to the motor, such as a motor drive connected to the motor, and a first resistance value of the winding. In exemplary embodiments, the motor drive and first resistance value are determined only after the motor has been idle for some predetermined time period. Once the calibration parameter is calculated, the processor uses it along with subsequent resistance measurements to calculate the temperature of the motor.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of and claims priority to U.S.patent application Ser. No. 12/714,133, now U.S. Pat. No. 7,908,893,filed Feb. 26, 2010, which claims priority to U.S. patent applicationSer. No. 10/906,305, filed Feb. 14, 2005, now U.S. Pat. No. 7,694,538.The present application is also a divisional of U.S. patent applicationSer. No. 10/906,305 filed Feb. 14, 2005, with continuity through U.S.patent application Ser. No. 12/714,133. The contents of each of theabove mentioned patent applications is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO APPENDIX

Not applicable.

BACKGROUND OF THE INVENTION

The present invention relates generally to sensing the temperature of arotating electromagnetic machine such as an electric motor or generator.

In many applications for rotating electromagnetic machines, thetemperature of the machine must be monitored and managed. For instance,clothes washing machines are typically powered by an electric motor.Residential and commercial clothes washing machines are well known. Agenerally cylindrical drum or basket for holding the clothing and otherarticles to be washed is mounted within a cabinet and rotated by theelectric motor. During a wash cycle, water and detergent or soap areforced through the clothes to wash them. The detergent is rinsed fromthe clothes, then during one or more spin cycles the water is extractedfrom the clothes by spinning the drum.

Vertical-axis washing machines have the drum situated to spin about avertical axis. Articles to be washed are loaded into the drum through adoor, which is usually situated on the top of the washing machine. Avertical-axis washing machine drum includes an agitator situatedtherein, which cleans clothes by pushing and pulling them down into thewater. Horizontal-axis washing machines have the drum oriented to spinabout an essentially horizontal axis. During wash cycles, the drum ofthe horizontal-axis washing machines rotates at a relatively low speed.The rotation speed of the drum is such that clothes are lifted up out ofthe water, using baffles distributed about the drum, then dropped backinto the water as the drum revolves. In some washing machines, therotation direction is periodically reversed to get the desired washingaction.

Both vertical and horizontal-axis washing machines extract water fromclothes by spinning the drum, such that centrifugal force extracts waterfrom the clothes. It is desirable to spin the drum at a high speed andextract the maximum amount of water from the clothes in the shortestpossible time. Spin time is reduced, but more power is required to spinat a higher speed.

When the washing machine drum contains a large load, the motor worksharder to rotate the drum. Economically sized motors can get too hot ifrun continuously at high power, as may occur with a large load. Poweruse can be modulated to control temperature, if the temperature isknown. Unfortunately, adding hardware for sensing the motor temperatureadds cost and complexity to the system. A sensorless means fordetermining motor temperature is therefore desirable.

The present application addresses shortcomings associated with the priorart.

SUMMARY

In accordance with certain teachings of the present disclosure, a systemand method of determining the temperature of a rotating electromagneticmachine such as an electric motor or generator is provided. The machine(hereinafter referred to simply as “the motor”) includes an energizablewinding connected to receive power from a power source. A temperaturecalibration parameter is calculated based on the temperature of anobject situated close to the motor, such as a motor drive connected tothe motor, and a first resistance value of the winding. For example, atypical motor drive includes a heatsink with a temperature measurementdevice is connected thereto. This can be used to measure the temperatureof the motor drive.

In exemplary embodiments, the motor drive and first resistance value aredetermined only after the motor has been idle for some predeterminedtime period. A processor, which may be a component of the motor drive,is programmed to determine the resistance value and to calculate thecalibration parameter based on the resistance value and a measuredtemperature of the motor drive. Once the calibration parameter iscalculated, the processor uses it along with subsequent resistancemeasurements to calculate the temperature of the motor. In applicationswhere the processor does not receive continuous power and thus cannotmonitor the idle time, an external component, such as a machinecontroller, determines whether the predetermined time period haselapsed. The winding resistance can be determined by applying current tothe winding and determining a voltage level required to maintain thecurrent at a desired level.

A suitable application for the temperature sensing method and system isin a clothes washing machine system that includes a cabinet with a drumsituated to rotate inside the cabinet. The motor is operably connectedto the drum to rotate the drum. Based on the temperature determinations,operation of the motor can be varied to avoid over heating.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to thedrawings in which:

FIG. 1 is a perspective view of an exemplary washing machine systemembodying certain aspects of the present disclosure.

FIG. 2 is a block diagram schematically illustrating components of thesystem shown in FIG. 1.

FIG. 3 is a block diagram further illustrating portions of the systemshown in FIGS. 1 and 2.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and are herein described in detail. It shouldbe understood, however, that the description herein of specificembodiments is not intended to limit the invention to the particularforms disclosed, but on the contrary, the intention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure.

As noted above, temperature must be monitored and managed in manyapplications using rotating electromagnetic machines, such as electricmotors and generators. For sake of simplicity, the term “motor” refersto rotating electromagnet machines. An example of such an application isa clothes washing machine powered by an electric motor. FIG. 1illustrates an exemplary washing machine 101 embodying various teachingsof the present disclosure. The washing machine 101 shown in FIG. 1 is ahorizontal-axis machine, having a drum 102 situated in a cabinet 104.

FIG. 2 is a simple block diagram illustrating certain of the componentsof the washing machine 101. A washing machine controller 110 receivesand provides inputs and outputs to control the various operations of thewashing machine. It is connected to a motor drive 112 that controlsoperation of an electric motor 120, which drives the drum 102.

FIG. 3 illustrates additional aspects of the motor drive 112 and motor120. In exemplary embodiments, a three-phase induction motor isemployed. The motor 120 includes a stationary member, or stator 122,that has a plurality of windings 124 disposed therein. In the disclosedembodiment, the windings 124 comprise copper wire. A rotating member, orrotor 126, is situated within the stator 122 to rotate relative thereto.In a three-phase induction motor, a rotating magnetic field isestablished by applying three-phase sinusoidal alternating voltages tothe stator windings 124 to effect rotation of the rotor 126.

The motor drive 112 includes a processor 130 and a power module 132, andit receives power from the washing machine control 110 via a main powerline 134. The power module is connected to the motor 120 to energize thewindings 124 to operate the motor. A communications line 140 isconnected between the washing machine controller 110 and the motordrive's processor 130.

When the washing machine drum 102 contains a large load, the temperatureof the motor 120 increases as it works to rotate the drum 102. As notedabove, it is thus desirable to monitor the temperature of the motor 120.It is well known that resistance in a wire, such as the motor windings124, is dependent on temperature. The definition of temperaturecoefficient, α=(R−R0)/R0*(T−T0), where R and R0 are resistances and Tand T0 are temperatures, leads to the modelT=kR+T1

which can be rewritten ask=(T−T1)/R  (Equation 1)

where k is a calibration parameter, T is the temperature of the motor120, R is the resistance of the windings 124 and T1 is a temperatureconstant.

The resistance R of the winding 124 can be measured by putting aconstant current through the winding 124 and measuring the voltagerequired to maintain the desired current. In the exemplary embodiments,the terminal voltage is measured and compensated for other componentsincluded in the power module 132 as necessary. The voltage is suppliedto the motor 120 by a pulse-width modulated (PWM) inverter bridgeincluded in the power module 132. The PWM voltage required to maintainthe constant current is averaged over some predetermined number ofsamples (4,800 samples at 16 kHz in one implementation).

The temperature T1 in the model is a constant and is a characteristic ofcopper.

Data from the CRC Handbook of Chemistry and Physics, 49th Edition, forresistance of copper wires at temperatures from 0 to 75° C. was fit toequation 1 by linear regression to obtain T1=−233.9° C.

In the population of motors used in a particular washing machineapplication, the winding resistance at room temperature varies so muchthat it would correspond to a temperature variation of about 70° C. asdetermined by a resistance measurement. That variation is too large tobe acceptable, so the calibration constant k must be adjusted for eachmotor. In the washing machine manufacturing process, or in washingmachine service repairs, it is costly and unreliable to make a manualadjustment of k; therefore, an automatic means of calibrating thetemperature measurement is desirable.

Once the motor has been idle for some period, it can be assumed that themotor has cooled to ambient temperature. Once the motor temperaturereaches ambient, it can be assumed that the temperature of the motor isthe same or nearly the same as another object in close proximity to themotor. Thus, if the temperature of the object in close proximity to themotor can be determined, this temperature can be used for thetemperature calibration.

In many motor applications, such as the washing machine applicationdescribed herein, the motor drive 112 is situated close to the motor.The motor drive's power module 132 includes a heatsink temperaturesensor 142 to monitor the temperature of the power module 132 andprevent damage to its electronic components due to overheating. Inaccordance with teachings of the present disclosure, the power moduleheatsink temperature sensor 142 is used to establish that the motor 120is at a particular temperature since the motor 120 and the motor drive112 are physically located close to each other in the washing machine101.

The heatsink in the motor drive 112 and the motor 120 likely havedifferent thermal time constants and heating rates—it cannot be assumedthat the heatsink located in the motor drive 112 and the motor wouldalways be the same temperature. To be sure that the motor is at the sametemperature as the drive, some predetermined time period must elapsesince the motor was powered before the calibration process is executed.In one implementation, the time period is two hours.

In a washing machine application, the motor drive 112 isn't continuouslypowered so it cannot keep track of the idle time for a long period.However, the washing machine controller 110 is typically continuouslypowered (the washing machine itself is typically continuously connectedto mains power). So the machine control 110 can determine whether therequired time period has elapsed since the motor 120 was last powered.When the washing machine controller 110 powers up the motor drive 112,it sends a message meaning “OK to calibrate” to the drive if thepredetermined time period has elapsed. The motor drive 112 thencalculates a value for the calibration parameter k using the heatsinktemperature value T_(heatsink) for the motor temperature and thecorresponding winding resistance value R as follows:k=(T _(heatsink)+234)/R

As described above, R can be measured by putting a current pulse throughthe winding 124 and measuring the voltage required to maintain thedesired current. This new value for k is stored in the motor drivenon-volatile memory, and used for further motor temperature calculationsbased on subsequent winding resistance measurements.

Accordingly, if the calculated temperature exceeds some predeterminedvalue, corrective action can be taken. For example, in one exemplarysystem, the drum rotation direction is periodically reversed. If thetemperature exceeds a first temperature limit, a waiting period is addedor increased before changing the rotation direction to allow the motorto cool. If the temperature exceeds a second limit, the motor is shutdown and an alarm is activated.

The particular embodiments disclosed above are illustrative only, as theinvention may be modified and practiced in different but equivalentmanners apparent to those skilled in the art having the benefit of theteachings herein. Furthermore, no limitations are intended to thedetails of construction or design herein shown, other than as describedin the claims below. It is therefore evident that the particularembodiments disclosed above may be altered or modified and all suchvariations are considered within the scope and spirit of the invention.Accordingly, the protection sought herein is as set forth in the claimsbelow.

What is claimed is:
 1. A method of controlling a temperature of arotating electromagnetic machine, the machine including an energizablewinding, the method comprising: waiting for the machine to be idle for apredetermined time period; determining a resistance value for thewinding; determining a temperature of an object within a cabinet of themachine, wherein the object is not the winding; calculating atemperature calibration parameter based on the resistance value and thetemperature of the object; calculating a temperature of the machinebased on the calibration parameter; and taking a corrective action toavoid overheating when the calculated temperature exceeds apredetermined temperature.
 2. The method of claim 1, wherein the objectis a motor drive.
 3. The method of claim 1, wherein the object is amotor drive having a heatsink, and wherein determining the temperatureof the object comprises determining a temperature of the heatsink. 4.The method of claim 1, wherein the temperature calibration parameter iscalculated from a characteristic of the winding, the resistance valuefor the winding, and the temperature of the object.
 5. The method ofclaim 1 wherein the corrective action is adding a waiting period beforechanging a direction of rotation in the machine to allow the machine tocool.
 6. The method of claim 1 wherein the corrective action isincreasing a waiting period before changing a direction of rotation inthe machine to allow the machine to cool.
 7. The method of claim 1further comprising, taking an additional corrective action if thecalculated temperature exceeds a second predetermined temperature limitto avoid damage from overheating, wherein the additional correctiveaction is shutting the machine down.
 8. The method of claim 7 whereinthe additional corrective action further comprises activating an alarm.